Starter for a gaseous discharge device



Jam 27, 1959 D. FL ALDRlcH ET AL 2,871,409

STARTER FQR A GASEOUS DISCHARGE DEVICE v Filed Deo. 24, 1954 Fig.3.

Fig.2.

hu. C e .H w wm O A T .E N F m Edu V mi mn Mw 6 S E s S F- N .J w

ATTORNEY States STARTER FR A GASEGUS DISCHARGE DEVICE Donald F. Aldrich, Elmira, N. Y., and William E. Newell, Penn rlownship, Allegheny County, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh,

Our invention relates to a starter for a gaseous discharge device and, more particularly, to a lamp started for iluorescent lamps using semiconductor elements.

As is well known, it has been the general practice to start some gaseous discharge devices, such as fluorescent lamps, by passing a preheating current through the cathodes at each end of the lamp in order to partially ionize the gas within the lamp, whereby a lower voltage may may be utilized to cause a discharge to occur across the device. In such lighting circuits, it has also been the general practice to connect the cathodes to a source of power and together in series with a starter switch of a suitable type, such as a glow type switch, in the series circuit. The starter switch has provided means fordisconnecting the series circuit in order to initiate a discharge across the lamp. Once such a discharge has occurred across the lamp the starter switch remains open. Although such starters have been commercially developed so that they are inexpensive and easily installed, they have had certain objectionable features. In particular, such starters have permitted the preheating current to tlow through the cathodes for a relatively long time in order to insure, as much as possible, that the lamps which have deteriorated to some degree will also `be started. inasmuch as the condition of the lamp with which a starter is to be used is unknown, a considerable time lag has been provided by the starter before a discharge will occur across the lamp so as to insure starting all lamps. Further, as such switches usually employ a glow discharge device and an arcing Contact, which elements have a relatively limited life, the cost of maintenance has vbeen objectionably high notwithstanding the low initial cost of thel starter. Such maintenance cost has particularly been objectionable in cases where a large number of lamps are utilized and a starter employed with each lamp.

Accordingly, one object of our invention is to provide a new and improved starting means for a gaseous discharge device,'the starting time of which adapts itself to the individual lamp automatically.

Still another object of our invention is to provide a new and improved iluorescent lamp starting means having only stationary elements.

A further object of our invention is to provide a new and improved starting means for gaseousl discharge devices which has stationary elements havinga breakdown voltage which is less than the starting voltage, but greater than the voltage required to operate thedischarge device.

Another object of our invention is to provide a new and improved fluorescent lamp starting means incorporating semiconductor elements.

Another object of our invention is to provide a new and improved uorescent larnp starter having semiconductordiodes connected in inverse series.

Yet another object of our invention is to provide a new and improved fluorescent lamp starter having stationary elements with a non-linear resistance.

Another object of our invention is to provide a new and improved iluorescent lamp starter having a plurality of seriesy connected semiconductor diodes connected in inverse series. y

These and other objects of our invention will become more apparent when taken in conjunction with the attached drawings and following detailed description of preferred embodiments thereof, in which: l Figure l'isv a circuit diagramfor a uorescent lamp having a starter constructed in accordance with the principles of our invention connected in series with the cathodes of the lamp; 4

Fig. 2 is a characteristic curve of current as a function of voltage for a semiconductor diode;

Fig. 3 is a characteristic curve of current as a function of voltage for a pair of semiconductor diodes connected in inverse series; y

Fig. 4 is a circuit vdiagram for a uorescent lamp having another starter constructed in accordance lwith the principles vof our invention and connected in Aseries with the cathodes of the lamp; and

Fig. 5 is a circuit diagram for a iluorescent lamp having the starter as shown in Fig, l with novel means for limiting the current flowing therethrough. Y

As shown in Fig. '1, a gaseous discharge device, such as a commercially available fluorescent lamp 2, which is adapted to be used with a starter constructed `in accordance with the principles of our invention, comprises an elongated sealed tube 4 having a cathode 6 at each of its ends. ln order to obtain a current ow through the vcathodes 6, each cathode 6 is connected at' eachxo'f its ends to an outwardly extending contact pin 8. Inasmuch as the construction of such lamps 2 is well known in the art, it is not believed necessary to further describe their construction or the various types of atmospheres that may be utilized within the tube 4. ,The contact pins S are adapted to be received by a lampholder 10 which may be of any` well known construction, such as, for example, those shown lin `Patents 2,456,940 and 2,268,708, and which includes a pair oflspaced electrically insulated contact lingers 12, veach of whichcngagesone of the contact'pins 8 of lamp 2. As 'is customary, each contact pin 12 is connected to electrically separated terminals 14 to which electrical connections may readily be made. As also shown, a source of suitable power l 16 is connected to a terminal 14 at each end of lamp 2 by means of conductors 18 and 20. Inasmuch as lamp 2 has a `negative resistance characteristic, a current limiting ballast 22, such as a high reactance' ballast coil, is electrically connected in series with either supply conductor, such vas conductor 20. vThe other terminal 14 of one lampholder lil is electrically. connected by a conductor 24 toa starting device constructed in accordance with the principles of our invention, which, in turn, is connected by means of a conductor 25 to the other terminal 14 of the other lampholder 10.` Y

As also illustrated in Fig. l, the starter device comprises a pair of semiconductor diodes 26a and 26b of well known construction, each having a cathode 28 and an anode 30, which are connected in inverse series and in series with the conductors 24 and 25. Although, as shown, the anodes 30 are electrically connected together by suitable means, such as a conductor 32, it will be realized that, if desired, the' eathodes 28 could be so connected together. Also, if desired, rather than utilizing a pair of diodes, a specially constructed double diode, such as two point contacts on a single basepa PNP, or NPN junction transistor, may be used.

lt is well known in the art that the eifectiveness of semiconductor diodes is, for some purposes, best indicated by the ratio of the impedance presented by the diode to current flow in one direction therethrough to that of current ow inthe other direction. Referring to isw'ell known that the amount of selected impurities Lwithin a semiconductor diodewill cause the value' of the voltage peak Er, to Vary, and, accordingly, a semiconductor L diode must be designed and constructed with reference to v its contemplated use. The voltage peak En for a paruticular semiconductor ldiode is not one given value, but

may be one of several values, which are primarily dependent upon the ambient temperature at which the semiconductor diode is operated. Thus, the characteristic curve asrshown in Fig. 2 is the characteristic curve at only one particular ambient temperature. Although other characteristic curves could be shown, they are generally similar to the curve shown in Fig. 2, however, the par'- ticular characteristic curve of Fig. 2 is particularly advantageous as will be more fully described hereinafter. It should also be noted that the leakage current of a diode ca uses the temperature of the diode to increase, which will also afect the Icharacteristic of a particular diode at a particular ambient temperature.

As has been indicated, a starter constructed in accordance with the principles of our invention, and as shown.

1n Flg. l, comprises a pair of semiconductor diodes 26a and 26b connected in inverse series. It is to be realized that the polarities of the voltages applied to diodes 26a and 26h are constantly changing due to the cycle nctuations of the alternating current source. For purposes of discussion, when an electron current I is owing, as indicated, through the diodes 26a and 26h, the diodes 26a and 26h have an instantaneous polarity as indicated; that is, the cathode 28 of diode 26a is at a positive potential with respect to its anode 30, and the cathode 28 of diode 26b is `at a negative potential with respect to its anode 30.

Under these circumstances, the diode 26h offers a comparatively' low impedance vto current flow therethrough. The diode 26a, however, will block any appreciable current flow therethrough until Aa voltage greater than the voltage peak Ep is applied thereacross.

i Referring now to Fig. 3 in which the characteristic nected diodes 26a and 2627 until the voltage peak Ep of diode 26a is exceeded. Once the voltage Ep of diode 26a 1s exceeded, the low forward impedance of diode 26h per lse would not prevent the current from flowing therethrough. Conversely, the impedance of 26a is low in the opposite direction, and the high reverse impedance of t? diode 26h will prevent any substantial current from being passed therethrough until the voltage peak Ep of diode 2Gb is exceeded.

By utilizing the inverse series combination of diodes y26a and 26b as shown in Fig. 3, for the starter as indicated 1n Fig. l, it will be noted that when an alternating currentis applied across the source 16 that, for a given half cycle, the forward impedance of diode 26a is low,

1 and it will not otter any substantial resistance to current ow therethrough. Diode 2617, however, does oifer a high resistance in such direction and will not permit any appreciable current to ow therethrough until the voltage peak Ep is exceeded. If, therefore, a supply voltage 16 equal to or greater than the voltage peak Ep is applied to the starter, the diodes 26a and 26h will pass current for a portion of one half-cycle after the instantaneous value of the supply voltage equals the voltage peak Ep. Under such conditions, a current will pass from one side of the supply line 16 through conductor 18, one terminal ,ldand its contact finger 12 and contact pin 8, to cathode 6, to the other contact pin 8, contact finger 12.y and terminal 14, conductor 24, diodes 26a and 26h, conductor 2S, to one terminal 14 at the other end of the lamp and its contact finger 12 and contact pin 8 to cathode 6, the other u contact pin 8 and its contact linger 12 and terminal 14,

conductor 20, through the current-limiting ballast 22 to the other side of the supply line 16. The situation is exactly the reverse for the reverse half cycle with the direction of currentow being the reverse of that previously indicated. Thus, it will be noted that current flows through the diodes 26a and 26h for only a portion of each half cycle and that the supply voltage is applied between the cathodes 6 of lamp 2 when there is substantially no current flow through the starter 26.

As is well known in the art, the passage of current through cathodes 6 will cause the cathodes 6 to heat and emit electrons within the tube 4 of lamp 2 to a sufficient degree that the gas within tube 4 is partially ionized. Under such partially ionized condition, the discharge in tube 4 may be started with a lower voltage than is required for cold starting of the lamp 2. Thus, as the supply voltage 16 is intermittently applied between the cathodes 6, and once the tube 4 has been sutliciently ionized, the supply voltage 16 will cause a discharge to occur across the lamp 2 at a voltage equal to or less than the voltage peak Ep depending upon the characteristics of lamp 2.

It is, of course, obvious, as indicated, that the supply voltage 16 must exceed the voltage peak Ep in order to obtain a current flow through the cathodes 6. Once a discharge occurs across the lamp 2, it is desirable that the starter and the cathodes 6 of lamp 2 no longer draw any current. Accordingly, the voltage peak Ep should preferably exceed the voltage drop between the cathodes 6 of lamp 2 after the discharge thereacross has been initiated, whereby the diodes 26a and 26b will be operating in that portion of their characteristic curve (Fig. 3) between opposed voltage peaks Ep, wherein substantially no current will ow therethrough. -As the lamp 2 is in parallel with the starter circuit, the voltage across the diodes 26a and 26h will be the same as the voltage drop across the lamp 2, and as the voltage peak Ep is no longer attained across the diodes 26a and 26b, no substantial current will flow therethrough.

It should be noted that a design appropriately small for starters may have insuicient thermal capacity to carry current continuously in the event that the lamp 2 ages, and the voltage drop across the lamp 2 rises to a value in excess of the voltage peak Ep. Accordingly, if desired, a current limiting resistor 40 may be placed in series in the conductor 25, whereby damage to the diodes 26a and 2Gb is prevented under these circumstances. It is also possible to use a thermostatic delay switch to prevent such damage similar to those employed in the present glow type starters.

If desired, a series of diodes 26a and 2617 may be connected individually in series and then together in inverse series relationship as shown in Fig. 4, where three diodes 26a and three diodes 26b are connected in this manner, whereby a lamp having a higher starting voltage may be utilized. Under such circumstances, the voltage required to cause a current to flow will be the surn of the various voltage peaks Ep of the individual diodes 26a, or 2Gb, dependent upon the direction of current ow therethrough. Thus, as shown, the voltage required for obtaining a current tlow would be equal to the individual voltage peak Ep of the three diodes. Under some circumstances, the internal resistance of the various diodes 26a and 26b may be utilized as a current limiting resistance without requiring separate current limiting devices by providing the diodes-with sucient internal resistance. It is of course obvious that if desired, a combination of series-connected diodes connected in inverse series could be utilized in conjunction with a current limiting resistor similar to the current limiting resistor 40. Regardless of which circuit may be utilized, the considerations regarding the voltage peak Ep as previously discussed `are equally applicable.

In actual tests usingl a 40-watt fluorescent lamp with a ballast and applying a ll7 volt 60-cycle alternating current, a series pair of germanium point-contact rectiers connected in inverse series with another series pair of germanium point-contact rectiiiers, have given satisfactory operation of the lamp when a current limiting resistor 40 having a value of 400 ohms was utilized. When six diodes from a selenium rectifier rated at 100 milliamperes were used, as shown in Fig. 4, no current limiting resistance was necessary. It has also been found, as previously indicated, that the diodes of the point-contact type or of the junction-type of either germanium or selenium rectiers have proven to be satisfactory. It is, of course, to be realized that the particular values of the circuits as herein indicated are purely illustrative and are not to be considered as limiting in any aspect.

Such a starter utilizes the non-linear current versus voltage characteristics of a semiconductor diode whereby the diode passes a very low current until a certain breakdown voltage is achieved, and thereafter a high current. Although as heretofore described, the voltage peak Ep resulting from the ambient temperature characteristics of such diodes has been utilized for such purposes, similar characteristics of other material or other operating ranges can be utilized if desired. Thus, for example, rather than utilize the voltage peak Ep indicated, the Zener breakdown voltage of a semiconductor diode could be utilized. Or, if desired, a semiconductor diode operating on a combination of Zener breakdown which has a higher voltage peak Ep and ambient temperature voltage peaks Ep could be utilized. Also, a non-linear current-voltage characterl istic material having similar voltage peaks, such as a silicon carbide material, could be used. Regardless of which type of non-linear element may be used, all such elements will depend upon characteristics similar to those discussed.

It has been found that the characteristic curves similar to the curves shown in Fig. 2 are preferable over other characteristic curves of the same semiconductor diode when operated at other ambient temperatures. Primarily, it will be noted from Fig. 2 that the voltage peak Ep curves at a relatively high voltage which approaches the Zener breakdown voltage, and that the voltage drop across the diode decreases rapidly to a very low value with further increase of current ilowing therethrough. With such a semiconductor diode, the increased current flows through each of the cathodes 6 of the lamp 2, and as the diodes 26a and 26b have a low voltage drop, the cathode 6 will have a larger voltage drop, whereby the diodes will have a lower power consumption as compared to the cathodes 6. Some other characteristic curves of the same diodes having a higher voltage drop thereacross, such as the Zener breakdown voltage, and would not permit as large a heat dissipation by the cathode 6 as would be possible with a diode operating at the characteristic curve, as shown in Fig. 2. Also, a diode operating on the characteristic curve, as shown in Fig. 2, permits diodes having a lower current rating to be used.

Another modication of our invention is shown in Fig.

in the conductor 25 in series with the diodes 26a and 265, and a pair of separate secondaries 64, connected to the cathodes 6, respectively, of lamp 2. The operation of such a device is similar to that previously described except that when diodes 26a and 26b conduct a substantial current there is a current flow through the primary 62 which in turn causes a current to flow through each of the secondaries 64. Each secondary is connected across a cathode 6, so that the secondary current passes through the respective cathode 6 to which it is connected in the same direction as the heating current passing therethrough when diodes 26a and 26b are conducting a substantial current, thereby causing further heating thereof. As can be appreciated, such additional current ow through the cathodes 6 also causes the cathodes 6 to emit additional electrons whereby the chamber of the lamp 2 becomes ionized. inasmuch as the ionization of lamp 2 that is required for starting the lamp 2 is limited, the additional current from the secondary 64 decreases the current requirements of the diodes 26a and 26b. In order to obtain equal heating of each cathode 26, the secondaries 64 of the transformer 60 are made substantially identical to each other. The transformer 60 should be designed to provide an impedance match between the characteristics of the lampy cathodes 6 and the characteristics of the diodes 26a and 26b, whereby the cathodes 6 will again have a high voltage drop compared to the voltage drop across the diodes 26a and 26b as previously discussed.

Thus, it wiil be noted that a starter constructed in accordance with the principles of our invention utilizes certain characteristics of certain types of materials whereby no moving parts are required for the starter. Further, as the life of semiconductor elements is quite long, the maintenance cost is substantially decreased, and in view of the small size of such elements, they are easily installed at any convenient location within the lighting fixture, including the ballast assembly. Also, in View of such small size, if desired, such a starter may be produced so as to be readily removable, similar to the method employed with the present-day glow switches whereby present installations could be utilized as presently constructed to incorporate a starter constructed in accordance with the principles of our invention.

Although we have shown and described several modications of our invention in accordance with the patent statutes, we are aware that further modifications thereof are possible without departing from the broad spirit and scope of our invention. Accordingly, it is desired that our invention be not restricted except insofar as is necessitated by the prior art.

We claim as our invention:

l. An electrical circuit for starting and operating a gaseous discharge device comprising, a pair of spaced lampholders adapted to support a gaseous discharge device of a type having a cathode at each of its ends with each cathode connected in series with a pair of terminals at the adjacent end of the gaseous discharge device, each of said lampholders having spaced contacts engageable with the terminals at one of said ends of said discharge device, respectively, a supply circuit connected to one of said contacts cf said lampholders, respectively, -a single series starting circuit connected to the other contacts of said lampholders including a starter comprising semiconductor means having more than one junction connected in series in said starting circuit, said semiconductor means having a blocking voltage lower than that of said supply circuit and the open circuit voltage of said gaseous discharge device but higher than the voltage across said device when a discharge occurs therein.

2. An electrical circuit for starting and operating a gaseous discharge device comprising, a pair of spaced lampholders adapted to support a gaseous discharge device of a type having a cathode at each of its ends with each.

cathode connected in series with a pair of terminals at the said lampholders having spaced contacts engageable with the terminals at one of said ends of said discharge device, respectively, a supply circuit connected to one of said contacts of said larnpholders, respectively, a single series starting circuit connected to the other contacts of said `lampholders including a starter connected in series in than the voltage across said device when a discharge occurs therein.

3. An electrical circuit for starting and operating a gaseous discharge device comprisingoa pair of spaced lampholders adapted to support a gaseous discharge device of a type having a cathode at each of its ends with each cathode conected in series with a pair of terminals at the adjacent end of the gaseous discharge device, each of said lampholders having spaced contacts engageable with the terminals at one of said ends of said discharge device, respectively, a supply circuit connected to one of said contacts Vof said lampholders, respectively, a single series starting circuit connected to the other of said contacts of each of saidy lampholders, a starter comprising at least a pair of semiconductor diodes connected in inverse series in said starting circuit, said diodes having a blocking voltage lower than that of said supply circuit and the open circuit voltage oi said gaseous discharge device but higher than the voltage across said device when a discharge occurs therein and a current limiting means also connected in series with said starter in said starting circuit. l

4. An electrical circuit for starting and operating a gaseous discharge device comprising, a pair of spaced lampholders adapted to support a gaseous discharge device of a type having a cathode at each of its ends with each cathode connected in series with a pair of terminals at the adjacent end of the gaseous discharge device, each of said lampholders having spaced contacts engageable with the terminals at one of said ends of said discharge device, respectively, a supply circuit connected to one of said contacts of said lampholders, respectively, a single series starting circuit connected to the other contacts of said lampholders including a starter comprising semiconductormeans having more than one junction connected in series in `said starting circuit,` said semiconductor means having a blockingvoltagelower .than that of said supplyvcircuit and the open circuit voltage of said gaseous discharge device but higher than the voltage across said device when a discharge occurs therein and current limiting means comprising a transformer' having its primary also. connected in series in said starting circuit With said semiconductor device, and a pair ofsep'arate secondaries connected across the cathodes of said `gaseous discharge device, respectively.

5. An electrical circuit for starting and operating a gaseous discharge ,device having a pair of electrodes oppositely disposed on and sealed within the gaseous discharge device comprising, a supply circuit serially connected toAe'ach electrode, a single series starting circuit connected to s aid oppositely disposed electrodes including a starter comprising semiconductor means having more than one junction connected in series in said starting circuit, said semiconductor means having a blocking voltage lower than that of said supply circuit and the open circuit voltage of said gaseous discharge device hut higher than the voltage across said device when a discharge occurs therein.

6. An electrical starting circuit for a gaseous discharge lamp having a pair of electrodes disposed Within said gaseous discharge lamp and placed across a supply circuit, a single series starting circuit connected to said electrodes, said single series starting circuit comprising a plurality of series connected semiconductor diodes which arev connected in series With another plurality of series connected semiconductor diodes but in inverse relation therewith, and each plurality of series diodes having a blocking voltage lower than that of the supply circuit and the open circuit voltage of said gaseous discharge device but higher than the voltage across said device when a discharge occurs therein.

References Cited in the tile of this patent UNITED STATES PATENTS 

